1. Field of the Invention
The present invention relates to an optical sensor that detects (is sensitive to) light or rays and a method of manufacturing the optical sensor, and more particularly, to an optical sensor that comprises a photo-detection element or device and a light condensation or collection element for conducting light or rays to the photo-detection element, and a method of manufacturing the optical sensor.
2. Description of the Related Art
Various types of optical sensors each detecting light or rays have been put to practical use. An optical sensor detects light or rays by receiving light or rays radiated from an object to be measured at a photosensitive surface of its photo-detection element. In order to make higher the sensitivity of photo-detection of an optical sensor, it is required to collect light radiated from an object to be measured and to bring the collected light into incidence on the photosensitive surface of the photo-detection element of the optical sensor. For that reason, there is usually put in front of the photosensitive surface of a photo-detection element any light condensation or collection element for efficiently collecting light or rays radiated from an object to be measured and conducting only light within a specified wavelength range to the photosensitive surface thereof.
In the prior art, a lens, waveguide, wavelength filter or the like has been used as such light condensation or collection element. For example, in Japanese Unexamined Patent Application Publication No. 2001-281053 (P2001-281053A) that was published on Oct. 10, 2001, there is disclosed an infrared sensor in which a convex ceramic lens is provided in front of a photo-detection part thereof and infrared radiation or rays collected through the ceramic lens are directed toward the photo-detection part. In Japanese Unexamined Patent Application Publication No. 2001-349785 (P2001-349785A) that was published on Dec. 12, 2001 and Japanese Unexamined Patent Application Publication No. 2002-48646 (P2002-48646A) that was published on Feb. 15, 2002, there is disclosed an infrared sensor in which a binary lens is used as a condensing lens for infrared radiation or rays and a wavelength filter (an infrared radiation coating) that passes therethrough only infrared radiation in a specified wavelength range is formed on the binary lens. In Japanese Unexamined Patent Application Publication No. 2002-48637 (P2002-48637A) that was published on Feb. 15, 2002, there is disclosed an infrared sensor in which received infrared radiation is reflected by a concave reflecting mirror and the reflected infrared radiation is collected to bring it into incidence on the infrared detection element thereof, that is, an infrared sensor in which the photosensitive surface of the infrared detection element is positioned on the rear side of the infrared sensor and received infrared radiation is reflected and collected by use of reflection and condensation elements or parts to bring it into incidence on the photosensitive surface of the infrared detection element. In Japanese Unexamined Patent Application Publication No. 2002-48649 (P2002-48649A) that was published on Feb. 15, 2002, there is disclosed an infrared sensor that has a plurality of lenses and a plurality of infrared detection elements provided therein in order to keep the accuracy of temperature measurement even the case that the optical axis of the infrared sensor is somewhat out of alignment with the optical axis of incident infrared radiation. In Japanese Examined Patent Application Publication No. H05-28617 (P05-28617B) that was published on Apr. 26, 1993 and Japanese Unexamined Patent Application Publication No. H08-191800 (P08-191800A) that was published on Jul. 30, 1996, there is disclosed an infrared sensor that is provided with a waveguide for guiding infrared radiation by a predetermined distance toward the photosensitive surface of the infrared detection element.
Meanwhile, an artificial crystalline material in which mediums each having a different refractive index from one another are periodically disposed is called a photonic crystal, and attracts attention or is watched as a technology that realizes various high-grade optical control elements or parts such as, for example, an element or part showing a super lensing effect due to negative refractive index, an optical waveguide having an abrupt crook with low loss, a microminiaturized optical integrated circuit, etc., that are not realizable by use of known optical materials or substances. The photonic crystal can be used as a light collection or condensation element for electromagnetic wave in any wavelength region in principle by matching a period of refractive index to a wavelength of electromagnetic wave. At present, research on the photonic crystal is actively performed in the technical field of optical communications as a substitute or alternative device for an existing optical element. However, there is no announcement or report on a form or configuration of utilization of element in case of using the photonic crystal as a light collection element until now. The present invention relates to an optical sensor that uses an element having light collecting function in which a photonic crystal is used and a method of manufacturing the optical sensor. Further, hereinafter, an element having light collecting function in which a photonic crystal is used is referred to as photonic crystal lens.
In case a photonic crystal lens is used as a light collection element or part, if the photonic crystal lens per se is manufactured as a single element and the manufactured single element is combined with an infrared sensor or other device to form one body, there are needed steps of manufacturing both of the elements separately and thereafter integrating both after completion of precise alignment thereof. For this reason, there occur problems that the manufacturing process is complicated and the manufacturing cost becomes higher.
In addition, in order to improve the measurement accuracy of an optical sensor, to make the sensitivity thereof higher, to miniaturize the size or shape thereof, and to reduce the manufacturing cost, it is necessary to overcome such conditions that a light condensation or collection element and a photo-detection element must be located to come close to each other as much as possible or to be in contact with each other; a spot of collected light should be made smaller so as to be able to collect light sufficiently in the state that the light collection element and the photo-detection element are located to come close to each other as much as possible or to be in contact with each other; dependence on the incidence angle of light and sensitiveness on the optical axis must be lowered, or alternatively, the incidence angle must be limited to control the directivity depending upon uses thereof; required optical control elements or parts such as lens and wavelength filter should be integrated to manufacture them in one manufacturing process; the accuracy of positional alignment required to integrate the photo-detection element with the light condensation element should be improved; the manufacturing process can be simplified; and the like.